Email Composers in Email-to-Case

Salesforce is transitioning email editor for Case (to be clear, this is not for email in other standard or custom objects) to a modern editor based on HTML 5.
 
Existing Case Email Composer

New Case Email Composer

The new editor provides new features, including:

• Full-screen mode
• Printing
• Undo and Redo buttons
• Format painting
• Emoji picker
• Resizability
• A more responsive toolbar
• Smart copy-paste functionality

Large recipient lists are no problem now that you can drag—or copy and paste—recipients' email addresses, attachments, and inline images.

You can manually transition to the new editor by navigating to Release Updates in the setup menu and looking for Transition to the Lightning Editor for Email Composers in Email-to-Case. As per the current timeline, this needs to be completed before 1st Sep 2024.

Reference:

• Transition to the Lightning Editor for Email Composers in Email-to-Case